1. Field of the Invention
This invention relates to a method of inspecting the integrity of spot and seam welds and more particularly it relates to an ultrasonic, nondestructive method of inspecting spot and seam welds.
2. Description of the Prior Art
Heretofore, the inspection of spot and seam welds has been performed using visual, radiographic and ultrasonic methods; as described in the Metals Handbook (Metals Handbook, 9th Edition, Volume 17, “Nondestructive Evaluation and Quality Control”, ASM International, Metals Park, Ohio, September, 1989, pg. 335) and the Nondestructive Testing Handbook (Nondestructive Testing Handbook, 2nd Edition, Volume 7. “Ultrasonic Testing”, American Society for Nondestructive Testing, Columbus, Ohio, 1991, pgs. 10–12 and pgs. 557–566). The visual and radiographic methods reveal little or nothing concerning the fusion of these welds. The prior art ultrasonic method referred to in the literature is a pulse-echo method however is generally referred to as a ring down technique throughout the industry. It makes use of the reflected amplitude and the envelope formed in time by many multiple reflections. Basically an envelope of these reflections are used to indicate if the weld is fused or not. Destructive sampling techniques of welds have also been in use. This has been done by either separating the sheets with a chisel or with a tensile pull technique. Another destructive technique in common use cuts through the weldment, polishes and enhances the weldment so that the dimensions of the fused part of the weld can be measured optically. In this prior art, the dimensions of the weld are used to infer the weld quality. Because the ultrasonic method can penetrate a fused weld zone, the length of continuous fused section(s) can be measured and easily related to weld strength. Additionally, ultrasound is sensitive to common weld defects.
It would be advantageous to have a technique and system that includes the capability to accurately measure dimensions of fusion in the weldment and to determine the presence of weld defects. Using the dimensions of the fused sections as a quality indicator would make the ultrasonic process highly reliable and accurate and save on industrial injury which sometimes occurs during the expensive destructive quality tests of welds. The present invention provides such a technique and system.